package org.esjsoftware;

import java.io.IOException;

public class Base64 {
  private final static char ALPHABET[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/' };
  private static int valueDecoding[] = new int[128];
  static {
    for(int i=0; i<valueDecoding.length; i++) {
      valueDecoding[i] = -1;
    }

    for(int i=0; i<ALPHABET.length; i++) {
      valueDecoding[ALPHABET[i]] = i;
    }
  }

  private Base64() { }

  public static String encode(byte[] data, int offset, int length) {
    int i;
    int encodedLen;
    char[] encoded;
    encodedLen = (length + 2) / 3 * 4;
    encoded = new char [encodedLen];
    for(i=0, encodedLen=0; encodedLen<encoded.length; i+=3, encodedLen+=4) {
      encodeQuantum(data, offset + i, length - i, encoded, encodedLen);
    }
    return new String(encoded);
  }

  public static String encode(byte[] data) {
    return encode(data, 0, data.length);
  }

  private static void encodeQuantum(byte in[], int inOffset, int len, char out[], int outOffset) {
    byte a=0, b=0, c=0;
    a = in[inOffset];
    out[outOffset] = ALPHABET[(a >>> 2) & 0x3F];
    if(len > 2) {
      b = in[inOffset + 1];
      c = in[inOffset + 2];
      out[outOffset + 1] = ALPHABET[((a << 4) & 0x30) + ((b >>> 4) & 0xf)];
      out[outOffset + 2] = ALPHABET[((b << 2) & 0x3c) + ((c >>> 6) & 0x3)];
      out[outOffset + 3] = ALPHABET[c & 0x3F];
    } else if(len > 1) {
      b = in[inOffset + 1];
      out[outOffset + 1] = ALPHABET[((a << 4) & 0x30) + ((b >>> 4) & 0xf)];
      out[outOffset + 2] = ALPHABET[((b << 2) & 0x3c) + ((c >>> 6) & 0x3)];
      out[outOffset + 3] = '=';
    } else {
      out[outOffset + 1] = ALPHABET[((a << 4) & 0x30) + ((b >>> 4) & 0xf)];
      out[outOffset + 2] = '=';
      out[outOffset + 3] = '=';
    }
  }

  public static byte[] decode(String encoded) throws IOException {
    return decode(encoded, 0, encoded.length());
  }

  public static byte[] decode(String encoded, int offset, int length) throws IOException {
    int i;
    int decodedLen;
    byte[] decoded;
    if(length % 4 != 0) {
      throw new IOException("Base64 string length is not multiple of 4");
    }
    decodedLen = length / 4 * 3;
    if(encoded.charAt(offset + length - 1) == '=') {
      decodedLen--;
      if(encoded.charAt(offset + length - 2) == '=') {
        decodedLen--;
      }
    }
    decoded = new byte [decodedLen];
    for(i=0, decodedLen=0; i<length; i+=4, decodedLen+=3) {
      decodeQuantum(encoded.charAt(offset + i), encoded.charAt(offset + i + 1), encoded.charAt(offset + i + 2), encoded.charAt(offset + i + 3), decoded, decodedLen);
    }
    return decoded;
  }

  private static void decodeQuantum(char in1, char in2, char in3, char in4, byte[] out, int outOffset) throws IOException {
    int a=0, b=0, c=0, d=0, pad=0;
    a = valueDecoding[in1 & 127];
    b = valueDecoding[in2 & 127];
    if(in4 == '=') {
      pad++;
      if(in3 == '=') {
        pad++;
      } else {
        c = valueDecoding[in3 & 127];
      }
    } else {
      c = valueDecoding[in3 & 127];
      d = valueDecoding[in4 & 127];
    }
    if(a < 0 || b < 0 || c < 0 || d < 0) {
      throw new IOException("Invalid character in Base64 string");
    }
    out[outOffset] = (byte)(((a << 2) & 0xfc) | ((b >>> 4) & 3));
    if(pad < 2) {
      out[outOffset + 1] = (byte)(((b << 4) & 0xf0) | ((c >>> 2) & 0xf));
      if(pad < 1) {
        out[outOffset + 2] = (byte)(((c << 6) & 0xc0) | (d  & 0x3f));
      }
    }
  }
}